Automatic control of the liquid level for evaporators



R. A. HETZER 2,240,952 AUTOMATIC CONTROL OF THE LIQUID"LEV EL'FOR EVAPORATORS May 6 1941.

Filed June so, 1938 E s m Wm M 0 NL VT. WL 1T mm A U Patented May 6, 1941 AUTOMATIC CONTROL OF m LIQUID LEVEL roa EVAPOBATORS Russell A. Hetzer, Cincinnati, Ohio, assignor to The AmericanLaundry Machinery Company, Norwood, Ohio, a corporation of Ohio Application June 30, 1938, Serial No. 216,772

3 Claims.

My invention relates to evaporators or stills and more particularly to improved means for automatically regulating the supply of liquid thereto and the supply of a heating medium to vaporize the liquid therein.

'In dry cleaning systems in which a volatile or low boiling point solvent containing a chlorine compound, such as carbon tetrachloride or perchlorethylene or a petroleum derivative, such as:

naphtha or benzine is employed, it is the practice to renovate 'or reclaim used, solvent for reutilization in the treating process. For this purpose the used solvent is usually drained from the treating vessel into a sump tank which serves as a supply tank for a still or evaporator in which the liquid is vaporized at a pressure not materially exceeding atmospheric, the vapors being subsequently condensed and collected in a storage tank for reuse in the process.-

It is the aim of the present invention to provide an improved apparatus by means of which the liquid to be reclaimed may be automatically supplied to an evaporator of the kind described When the liquid surface in the evaporator falls to a predetermined level and by means of which a heating medium may be automatically supplied to evaporate the liquid in the evaporator when its surface rises to a predetermined level. Means also may be provided to automatically prevent a supply of heating medium to the evaporator when the surface of the liquid in a supply tank for the evaporator falls below a predetermined level.

It is, therefore, an object of my invention to provide an evaporator or still operating at a pressure not materially exceeding atmospheric and having. a chamber for volatile solvent liquid and a vapor space above said liquid in combination with automatic means responsive to the effect of both the liquid and the vapors in the chamber for supplying liquid to the evaporator when the liquid heat to" volatilize the liquid in said evaporator when its surface rises to a predetermined level, the supply of heat being shut ofi when the surpredetermined level and being withheld from the evaporator if the level of liquid in the supply tank i at or reaches an abnormally low level.

A further object of my invention is to provide an improved control device for evaporators or stills of the character described, which is actuated by the efiect of both the liquid and vapors in the evaporator, to supply liquid to the evaporator when the liquid surface in the evaporator falls to apredetermined level, and which is provided with cooling means tending to prevent the possibility of operation of the control device by the effect of the evaporator liquid alone.

My invention will be better understood by reference to the accompanying drawing, in which Fig. 1 is an elevation of an evaporator and a fragmentary portion of a supply tank, with parts broken away, and showing my improved control device in diagrammatic form applied to the evaporator 'and supply tank;

0 Fig. 2 is a sectional plan view on the line 2--2 of Fig. 1; and I Fig. 3 is a sectional elevation on theline 3-3 of Fig. 2. While my improved control device may heapplied to any evaporator or still which is adapted to be operated at a pressure or at.pressures at or below atmospheric, or, at least, not materially exceeding atmospheric, for purposes of illustration it is shown applied't'o the evaporator of a reclamatlon unit of a dry cleaning system to which liquid atmospheric pressure.

As shown in the drawing, the numeral 1 designates the evaporator having a chamber 2 to which liquid is supplied from a supply tank 3 through a pipe 4 controlled by a valve 5. While any convenient means may be provided for supplying heat to the liquid in the evaporator, as illustrated in the drawing it is heated by means of steam supplied to a coil 6 located in the bottom of the evaporator from a suitable source through a supply pipe I controlled by hand valve 8 and automatic valve 9, the steam from coil 6 being exhausted through pipe I0. Vapors from the still pass through the vapor pipe II to a suitable condenser, not shown, for recovery and reuse in the process, said condenser being open to atmosface of the liquid in the evaporator falls to a phere when the still is operated at atmospheric pressure, or being connected to vacuum producing apparatus when the still operates below atmospheric pressure, as will be readily understood.

In accordance with my invention, automatic means is provided for supplying liquid from supply tank 3 to the evaporator when the surface of the liquid in the evaporator fall to a predetermined level and for supplying steam to the heating coil 8 when the surface of the liquid in the evaporator rises to a predetermined level. For this purpose I provide the still with a generator type regulator, including an auxiliary container higher vapor pressure than .the liquid undergoing treatment. A conduit I8. connects chamber I So of the jacket I5 to a suitable operating device forming part of a controller, shown as a movable abutment II which, as illustrated, is in the form of an expansible and contractible hollow bellows sensitive externally to atmospheric pressure and internally to the pressure of the control fluid,

As shown in the drawing, the fluid in the jacket I5 is in heat exchange relationship with both the liquid and the vapor in container I2. In other words, it' crosses the liquid level line of the still. Therefore, the amounts of the vapor and the liquid of the still which are in heat exchange relation with the control fluid depend upon the level ofthe surface of the liquid in evaporator I. As willrbe seen from Fig. 3 of the drawing, as thesurface of the liquid in evaporator I falls, the amount of the vapor in heat exchange with the fluid. in jacket I5 increases and the amount of the liquid which is in heat exchange relationship with the fluid de creases. On the other hand, as the surface of the liquid in evaporator I rises, the amount of liquid which is in heat exchange relationship with the fluid in jacket I5 .increases and the amount of vapor in heat exchange relationship with'the fluid decreases. I

Because of the greater heat transfer ability of vapor, due to the latent heat of vaporization,

as the amount of vapor in chamber I211 in heat exchange relationship with the control fluid in chamber I50. increases, the vapor pressure of the control fluid likewise increases until finally it becomes suflicient to move abutment Ila sufflcient extent to operate the control device,

marked generally I3, of which it forms a part, which then becomes efiective to supply additional liquid to evaporator I. As the level of the surface of the liquid rises in evaporator l, however, the amount of liquid in chamber 32a which --by an adjustable screw 22 and a spring23 resting against abutment I1 and supporting a plunger 24. Arm 20 is connectedto one side of a block 25, a compression snap-acting spring 26 being attached to the other side of the block and the other end of the spring being secured 'to a block 21 supported by a bracket 28 on a wall of the casing. Extending upwardly fromarm 20 and connected at one end thereto, is a link 29 which is connected at its opposite end to one end of a bracket 30 supporting a mercury switch 3|, the bracket for the mercury switch being pivotally mounted to the casing at the point 32. As the vapor pressure of the control fluid in bellows Il increases, the plunger 24 raisesarm 20 which rotates bracket 30 and mercury switch 3| in a counterclockwise direction and compresses spring 26. As arm 20 passes dead center, spring 26 expands with a snap action and completes the rotation of bracket 30 and mercury switch 3|, thereby forming an electrical connection between terminals 33 and 34. When the vapor pressure in chamber I50. decreases,

however, spring 2| for'ces arm 20 in the opposite direction, rotating bracket 30 and mercury switch 3| in a clockwise direction and compressing chamber I5a is relatively low and abutment bel lows I1 is contracted. At this time current is being supplied from line L1 through conductor Ill) creases to a predetermined extent,' however, the

control device I8 is operated reversely and becomes effective to shut off the supply of liquid to the evaporator and to supply heat thereto.

31, terminal 36, terminal 35, and conductor 38 to normally closed switch 39 and from thence through conductor 40 to solenoid 4| and conductor 42 to line L2. 'The energized solenoid 4| has raised valve Sand steam is being supplied to the coil 6 to evaporate the liquid.

As the surface of the liquid in evaporator I falls, the amount of vapor in chamber I211 which is in heat exchange relationship with the control fluid in chamber I5a increases and the amount of liquid which is in heat exchange relationship with the control fluid decreases, thereby causing an increase in the vapor pressure of the fluid in chamber Ilia. Control bellows Il therefore expands forcing plunger 24 against arm 20, which moves the arm upwardly and rotates bracket 30 and mercury switch- 3| in the counterclockwise direction, the expansion of spring 26 completing the rotation of the bracket and mercury switch as the lever 28 passes the unstable position of spring 26. A circuit is thus established from line L1 through conductor 37, terminal 34, terminal 33, and conductor 43 to solenoid I 9 and by conductor 44 to line L2. Encrgization of solenoid I9 opens valve 5 and liquid flows from the sump tank 3 into evaporator I. As the level of liquid in the evaporator I rises, the proportion of liquid from evaporator I which is in heat exchange relation with the fluid in chamber |5a in-- cially where the operating device is of the movable abutment or expansible bellows variety internally to the pressure of the control fluid,

the control system as a whole must be of a character suitable to produce movement of the actuating device in accordance with fluctuations in level, in the generator type regulator, of the liquid being vaporized. The fluid in the closed control system must be of such a character, under the prevailing conditions, as to generate sufflcient pressure to cause operation of the actuating device against the load of its duty. Depending upon the character of the control mechanism, this duty may be the movement of valves, switches, relays, or like devices, springs, etc'. the arrangement shown in the drawing," the load or duty of the actuating devicev H, in addition to that of overcoming atmospheric pressure against which it operates, is that of overcoming the compression of loading spring 2| and snapacting spring 26, together with the friction of the moving parts of the mechanism.

When a still or evaporator is of the steam boiler variety, to-wit, one evaporating water, the still is usually operated under pressure, say one hundred pounds pressure per square inch above atmospheric. Excepting for losses of heat by radiation it is possible, in a generator regulator control system for a steam boiler, with water used as the control fluid in the closed system, to generate pressure of the control fluid approaching or of the general order of t e Pressure in the boiler. The control fluid pressure, for example, might be as much as seventy-five, pounds per square inch, and that pressure is more than amply sufficient to take care of any load or duty of the control device. v

The present invention, however, is not concerned with a still or evaporator operating at material or substantial pressures above atmospheric, such as in the case of a steam boiler. The still or evaporator here involved has no purpose of transferring either heat or pressure, but is designed solely for the purpose of evaporating or distilling, for purifying purposes, a volatile or low boiling solvent liquid, such as those heretofore referred to. While the present still or evaporator may be operated at a pressure slightly above atmospheric, say a few pounds, it is usually operated at atmospheric pressure or below atmospherici pressure. Even when the pressure is above atmospheric, it would not be sufficiently elevated above atmospheric to produce suflicient pressure in the closed control system to operate an actuating device and control mechanism, if the control fluid were identical with that being, vaporized in the evaporator or if the vapor pressure of the fluids in the evaporator and closed controlsy stemwere close together.

Accordingly, when the present still is used for any particular volatile or low boiling point liquid, whether it be one used as a solvent in a dry cleaning system as in my Patent No. 2,142,726, granted January 3, ,1939, or for'other purposes, I operate the still at a pressure or pressures not materially higher than atmospheric and utilize a control fluid whose vapor pressure is sufliciently higher than the vapor pressure of the liquid being reclaimed, so that assuming the pressure in the still to remain fairly constant, as

is the case when it is operated at substantially atmospheric pressure, suflicient pressure may be generated by the regulator in the closed control system to actuate the control device, including its actual load or duty, as above referred to,

When carbon tetrachloride is the liquid being reclaimed, ethyl ether has been found suitable for a control fluid because it has been iound that operating at a pressure which is not materially higher than atmospheric pressure when vaporizing carbon tetrachloride, ethyl ether in the closed control system will generate a pressure 'of substantially thirty-eight pounds per square inch, which, operating against atmosphere, effective externally on the bellows I1, is suiiicient to cause operation of the control mechanism.

Other control fluids having a sufficiently high vapor pressure to operate the control device at atmospheric pressure or not materially higher than atmospheric pressure also may be employed. For example, when carbon tetrachloride or trichlorethylene are being vaporized any one of the fluids, methylene chloride, methyl alcohol, ethyl bromide, acetone, or methyl formate, may be utilized as the control fluid. It will be noted that ingeneral these organic compounds have boiling points ranging approximately from 34 to 65 C., with corresponding vapor pressures.

Of course, in the distillation of certain liquids, reduced pressure or vacuum is employed. That is true, for example, in the distillation of certain petroleum distillateshaving a comparatively high boiling point, such as Stoddards solvent, with a boiling point of 420 F. In that case the control fluid again must be selected with a vapor pressure sufficiently higher than that of the liquid being reclaimed, in order to generate sufficient pressure in the closed control system to predetermined abnormal level. In such an event, it might be impossible to cause the surface of the liquid in evaporator l to rise to a suflicient level to cause immediate actuation of the control device for the purpose of closing valve 5 and supplying heat to the evaporator. Therefore, the liquid in the evaporator might cool and the vapors would condense due to the loss of heat by radiation, thus causing a decrease in the vapor pressure of the control fluid, and spring 2| might actuate the control device to supply heat to the evaporator. Since a further supply of liquid to the evaporator would not be available when the control device was actuated in the opposite direction, the liquid in the evaporator would eventually all be vaporized. For preventing this, the supply tank is provided with a float 45 through which the stem 46 of the switch 39 extends, the lower por. tion of stem 46 being provided with a. head 41. Under normal conditions when there is sufficient supply of fluid in supply tank 3, switch 39 is held .in closed position by means of a spring 48 interposed between the switch 39 and the top of the supply tank. However, if the surface of the liquid in the supply tank falls to an abnormally low level, float 45 engages head 41 opening the switch 39, which prevents the energization of solenoid 4| and valve 9 remains closed. Supply of heating medium to the evaporator, therefore, is prevented.

In the event that a control liquid is utilized which has such a high vapor pressure that sufflcient pressure to operate the control device might be generated in the control fluid by that portion of the liquid being vaporized which is in the generator regulator before the surface of said liquid falls to the desired level, means may be provided for cooling the liquid passing As illustrated, fins 49 are provided for this pur pose,'.upon the tube II which communicates with the liquid space of the evaporator and auxiliary container 12. Liquid from the evaporator passing into container I2 is consequently cooled,

which decreasesthe amount oi heat transferred from the liquid to the control fiuid and prevents the operation of the control device until the surface 01' the liquid in the evaporator falls to the desired level.

The invention described makes itipossible to evaporate low boiling point liquids, such as volalone to-cause suiiicient response in the generator type regulator to call for liquid supply when none is required.

Other advantages of the invention will be apparent to those skilled in the art.

What I claim is: 1. Apparatus of the class described comprising a supply tank containing a liquid to be vaporized, an evaporation chamber for said liquid, a'

source of heating medium for vaporizing said liquid, communicating means between said tank and said chamber, means responsive to the fall of the liquid surface in said chamber to a predetermined level during vaporization for automatically supplying liquid'from said supply tank to said chamber, means responsive to the rise of the surface'of the liquid in said evaporator to a predetermined level for supplying said heating medium to vaporize the liquid in said evaporator, and means responsive at a predetermined low level of the surface of the liquid in said from evaporator I into auxiliary container l2.

supply tank for preventing -a supply of heating medium to said vaporizing means.

2. Apparatus of the class described comprising a supply tank containing a liquid to be vaporized, an evaporation chamber for said liquid, a source of heating medium for vaporizing said liquid, communicating means between said tank and said chamber, means responsive to the fall of the liquid surface in .saidchamber to a predetermined level during vaporization for automatically supplying liquid from said supply tank to said chamber, means responsive,,to the rise of the surface of the liquid in said evaporator to a predetermined level for supplying said heating medium to vaporize the liquid in said evaporator, said means actuated by said fall and rise of liquid comprising a movable member responsive respectively to thevaporization and condensation of a volatile liquid, and means responsive at a predetermined low level of the surface of the liquid in said supply tank for preventing a supply or heating medium tosaicl vaporizing means.

3. Apparatus of the classdescribed comprising a supply tank containing a liquid to be vaporized, an evaporation chamber for said liquid. a source of heating medium for vaporizing said liquid, communicating means between said tank and said chamber, said apparatus being provided with a vapor outlet to maintain the chamber at substantially atmospheric pressure, means responsive to the fall of the liquid surface in said chamber to a predetermined level during vaporization for automatically supplying liquid from said supply tank to said chamber, means responsive to the rise of the surface of the liquid in said evaporator to a predetermined level for supplying said heating mediumto vaporize the liquid in said evaporator, and means responsive at a predetermined low level of the surface of the liquid in saidsupply tank for preventing a supply of heating medium to said vaporizing means.

RUSSELL A. HETZER. 

